(1) Field of the Invention
The present invention relates to a serial printer control system especially suitable for preparing a desired layout document by using a serial printer.
(2) Description of the Prior Art
Conventionally, when the serial printer is controlled by a host computer to carry out printing, it is necessary to create a complicated program with commands for specifying an operating position of a printing head and commands for controlling a paper feed quantity, so as to set a desired print format which makes a desired layout print. Therefore, a user is required to develop a private program for the purpose of preparing a document with a desired layout, which is inconvenient. Even if a specialized document preparing device, that is, a so-called word processor, can merely set a format selectively in a fixed range only, because it is hard to freely set and correct a print format.
Furthermore, as in both the above cases, unless the user precisely calculates a relation between a print paper and a print position in designing the print format, he cannot achieve printing at a desired position on the paper. Especially, in the case that print data are printed at predetermined positions on a preprinted paper, it is required to set the paper in the printer many times and repeat by trial and error to make a print format so that the print data may be printed at the predetermined position.
Further, it is preferable to easily and freely set a print pitch so as to prepare a document with a desired layout. But, the above-mentioned problems are also generated in the prior art.
Furthermore, even if the print format providing a desired printing layout is set, errors are frequently found after actual printing. The prior art systems make no provision for easily confirming the set print format prior to printing, and errors are found upon actual printing. In association with this, a print program must be reset and the print format must be corrected. Moreover, in the case when errors are found in the print format, or the print format is corrected as newly required, the prior art requires complicated steps. In addition, correction of only one print format data causes a requirement to correct the entire print format.
In a step of feeding paper to the printer, when crumpling and wrinkling of the paper, which will be referred to as paper jam, happens, a desired document cannot be prepared.
In the conventional serial printer, paper is fed into a small gap between a platen and a printing head along an outer circumferential surface of the platen. For smooth feeding of the paper, a carriage is provided with a paper holder, which also is called a scale, of a transparent plate arcuately curved along the platen with a small gap defined between the same and the platen. The paper is fed from a back surface of the platen along a lower surface to a partly cylindrical paper guide arranged at a fixed distance from the platen. The paper fed is ejected from a front portion of the platen through the printing head to bail rollers. Owing to the paper holder mounted to the carriage, the paper is smoothly introduced into the space between the platen and the printing head, is curvedly fed along the outer circumferential surface of the platen, and is upwardly guided between the paper holder and the platen. The paper guided by the paper holder is finally pressed on the platen by the bail rollers.
Accordingly, the paper holder mounted on the carriage has an important function for smooth introduction of the paper, and if it were not for the paper holder, smooth introduction of the paper would be almost impossible. It is preferable that the width of the paper holder is not greater than the carriage, since there is an unprintable area at both ends of the platen by the provision of the paper holder. The paper holder is provided with a window or a recess at a central portion, since a tip of the printing head is projected through the window or the recess. When the paper holder is located at a position out of the width of the paper upon insertion of the paper, the paper cannot be smoothly turned along the platen to cause a paper jam. In the case where a side edge of the paper is located at the central portion of the paper holder, a corner of the paper is caught by the window or the recess of the paper holder and the tip of the printing head to cause a paper jam. Furthermore, when the paper holder is located at the end of the paper with respect to the width of the paper, smooth feeding of the paper cannot be effected because of an unbalance caused by tension applied to the paper which results in a paper jam.
To avoid such problems, the carriage is moved to the longitudinal central position of the platen upon introduction of the paper. However, the amount of movement of the carriage is preset to an inherent value of the printer irrespective of a size of the paper, and cannot be changed. As the size of the paper is widely varied in the range of a post card size to an A3 size, for example, there is a possibility that the paper holder will not align to the paper or will come to the edge of the paper in dependence upon a width of the paper and a paper set position in the lateral direction of the platen. Therefore, this also causes a jam of the paper.